Topic 6 - Quantitative Chemistry Flashcards
What is relative atomic mass the same as and how can you work it out?
- Same as mass number
- Bigger number of the 2 of an element
How do you work out the relative formula mass?
Sum of each atom’s atomic masses
What is the equation to work out the percentage mass of an element in a compound?
Percentage mass of an element in a compound = (A~r x no. of atoms [of that element]) / M~r [of whole compound] ‘ x 100
How do you work out the empirical formula from masses?
- List all element in the compound
- Underneath write experimental masses
- Divide each by A~r for particular element
- Turn numbers into a simple ratio (may involve x or /)
- Use ratio to tell you empirical formula
How do you calculate masses in reactions?
- Write out balanced equation
- Work out M~r (just for bits needed)
- Divide to get one, multiply to get all (to substance given to work out other one)
What is the yield of the reaction?
Mass of the product it produces
How can you work out the theoretical yield of a reaction?
Balances reaction equation
What is the equation to work out the percentage yield?
percentage yield = actual yield, g / theoretical yield, g ‘ x 100
Why is the percentage yield always less than 100%?
- Incomplete reactions (not all reactant converted to product)
- Practical losses during preparation (lose some when transferring chemicals between containers)
- Unwanted reactions (can be caused by impurities or changing reaction conditions, decreases amount of intended product)
What are the ideal circumstances for chemical reactions in industry to maximise profit?
- High percentage yield
- All product commercially useful so no waste
- Suitable speeds, quickly + safely
Why do people not want waste products from reactions in industry?
- Aren’t profitable as not commercially useful
- Can be harmful, threat to people/environment; disposing safely can be expensive
